1. Field of the Invention
This invention relates to concrete-pumping machines and, more particularly, to an improved constant-flow valve assembly for concrete pumps.
2. Description of the Prior Art
At the present time, there is a great variety of concrete-pumping machines, each of these various types of machines having certain features and principles common with the others. However, all of these devices have the inherent problem of not being able to provide a constant flow of concrete.
Since the invention of concrete-pumping machines, there has been a search for low-maintenance, reliable and effective means to eliminate surge, and the accompanying jumping or shaking of the discharge hose. The continuous or constant flow of concrete has been the object of many patents issued in a field that has become crowded by attempts to arrive at some satisfactory means to accomplish that constant flow.
Oitto, U.S. Pat. No. 1,533,333, as early as 1925, discovered that alternately activated cylinders would produce a constant water flow.
Kirby, U.S. Pat. No. 2,033,338, disclosed in 1936, the use of a hydraulic cylinder to pump cement, grout or concrete, his cylinder being alternately moved between the material opening and discharge tube.
Since prior pumps became clogged in use, Logenecker, U.S. Pat. No. 2,485,208, proposed in 1949 a method introducing a water source behind the concrete-pump piston and the concrete-outlet line which could be used to clean out the apparatus.
In 1951 U.S. Pat. No. 2,548,733, disclosed a valve assemble to enable two cylinders to alternatively pump concrete, although his claims were directed to means for feeding concrete to the pump.
Pape, U.S. Pat. No. 2,690,715, in 1954 proposed a flap-and-slide valve to maintain a "pressure head" of concrete by synchronizing the discharge of two or more pumping cylinders.
More recently, Triebel, U.s. Pat. No. 2,998,781, used slide valves to alternately charge and discharge a pair of pumping cylinders; and Schwartz, U.S. Pat. No. 3,146,721, by means of his slide-valve synchronous mechanism, sought to attain constant pressure and uniform flow.
U.S. Pat. Nos. 3,198,123; 3,266,433; 3,266,435; 3,279,382 and 3,279,383 disclosed a number of different cylinder/valve combinations paired with control means of various kinds, attempting to achieve a practical constant-flow, concrete-pump mechanism.
Sherrod teaches in his patents, U.S. Pat. Nos. 3,298,322 and 3,380,3883,389,388, rotatable curved valves and improved synchronizing systems, attempting to produce a device that has truly no surge and constant flow.
Schwing, U.S. Pat. No. 3,580,696, uses a pair of flap valves to control the output of two cylinders into a single outlet and provides means to synchronize the oscillation of these valves.
Stetter, U.S. Pat. No. 3,628,897, and other use rotary valve mechanisms which are not pertinent to this discussion but are of interest in that they illustrate the various approaches used in an attempt to solve the problem inherent in a constant-pressure, continuous-flow, concrete-pumping mechanism.
Cole, U.S. Pat. No. 3,650,638, and Antosh, U.s. Pat. No. 3,663,129, introduce the concept of three or more concrete-pump cylinders synchronously operating to reduce the time interval required for the valves to operate.
Antosh has an auxiliary cylinder which enables him to maintain communication between a discharging concrete-pump assembly and the outlet duct at all times. His valve, however, is an enlarged chamber which must encompass the outlets of at least two concrete-pumping assemblies at all times. This enlarged valve in practice is a source of packing and accumulation of large aggregate, thus causing clogging of the mechanism. Flow characteristics of the concrete from the cylinder-discharge opening to the outlet duct is less than optimum because of the large-volume valve and relatively small outlet opening.
Guddal, et al., U.S. Pat. No. 3,683,575, introduces a Y-shaped fitting to control the flow of concrete through the pump from two discharge cylinders. His prior art is of interestin that he recognizes a Y-shape as being more efficient than Antosh's enlarged valve means. However, Guddal uses a slidable valve spool to connect the outflow of the cylinder to each leg of the Y, and his invention fails to achieve the constant-pressure, continuous flow for surges occuring during the interval the valve is moving from one leg of the Y to the other.